I'm failing to understand why [1] mentions "table-rewriting forms of ALTER TABLE" besides TRUNCATE command.
For TRUNCATE it seems clear: if transaction A takes the snapshot before it accesses the table first time (typically because isolation level is at least REPEATABLE READ) and transaction B manages to commit TRUNCATE soon enough, then A sees pg_class entry of the table already affected by B, which has the new (empty) relfilenode. (The original pg_class entry is no longer visible by catalog snapshot, nor does it contain valid OID of the original relfilenode.) But IMO heap rewriting changes neither table contents, nor visibility. Can anyone explain what I miss? [1] https://www.postgresql.org/docs/9.6/static/mvcc-caveats.html -- Antonin Houska Cybertec Schönig & Schönig GmbH Gröhrmühlgasse 26 A-2700 Wiener Neustadt Web: http://www.postgresql-support.de, http://www.cybertec.at -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
